1. Field of Invention
The present invention relates to a projector for projecting and displaying an image.
2. Description of Related Art
In a projector, image light representing an image is formed from illumination light using an electrooptic device, and an image is displayed by projecting the image light. As the electrooptic device, an optical modulation device (emitting direction control-type optical modulation device) for modulating the illumination light according to the image information (image signal) and emitting the image light representing the image, is used. As an example of the optical modulation device, a micro-mirror-type optical modulation device, such as a Digital Micro-mirror Device (registered trademark of Texas Instruments, Inc.; hereinafter, referred to as xe2x80x9cDMDxe2x80x9d) can be given.
The DMD has a plurality of micro-mirrors corresponding to a plurality of pixels constituting the image. The inclination of the micro-mirrors varies with image information, and the micro-mirrors reflect light according to the inclination thereof. Of the light reflected by the micro-mirrors, the light reflected in a predetermined direction is used as the image light. That is, the DMD is an electrooptic device of a type which controls the direction of reflection of light so as to form image light.
FIG. 13 is a schematic plan view showing a construction of a principal part of a conventional projector using a micro-mirror-type optical modulation device. A projector 5000 includes an illuminating optical system 100E, a micro-mirror-type optical modulation device 200, and a projection lens 300.
The illuminating optical system 100E includes a light source 110, a first condenser lens 120, a color wheel 130, a light-transmitting rod 180A, and a second condenser lens 190.
The light emitted from the light source 110 passes through the first condenser lens 120, the color wheel 130, the light-transmitting rod 180A, and the second condenser lens 190 to enter the micro-mirror-type optical modulation device 200. The light entered the micro-mirror-type optical modulation device 200 is modulated according to an image signal given to the micro-mirror-type optical modulation device 200. The light modulated by the micro-mirror-type optical modulation device 200 is projected as light representing an image (image light) via the projection lens 300, whereby an image is displayed.
There may be many cases where illuminance distribution of the light emitted from the light source 110 is not uniform. When such light is used as illumination light, there may be many cases where the brightness of the displayed image is not uniform according to the illuminance distribution of the illumination light. However, an image displayed by a projector may preferably have uniform brightness and be bright. Thus, in order to solve the problem, the light-transmitting rod 180A has been often used as in the illuminating optical system 100E. The light-transmitting rod 180A is an optical element having the function of emitting light whose illuminance distribution is uniform even if the illuminance distribution of incident light is not uniform.
The light-transmitting rod 180A is, however, an optical element in which light entered from an incident-side side surface 180AI of the light-transmitting rod 180A passes through the light-transmitting rod 180A while being repeatedly reflected by the inner surface of the light-transmitting rod 180A, thereby producing a uniform illuminance distribution of light emitted from a side surface 180AO on the side of an emitting surface. Therefore, in order to produce a uniform illuminance distribution of the light emitted from the light-transmitting rod 180A, the light entered the light-transmitting rod 180A must be reflected many times by the inner surface of the light-transmitting rod 180A. That is, the light-transmitting rod 180A requires a length according to the illuminance distribution of the light emitted from the light source 110, and the longer length is more preferable. Consequently, in a projector which utilizes an illuminating optical system using a light-transmitting rod, the length of an optical path of the illuminating optical system (physical length of the optical path between a light source and a micro-mirror-type optical modulation device) is generally elongated, causing a problem in that a reduction in size of the device is difficult.
Incidentally, the brightness of the image displayed by the projector greatly depends on the illuminance of an illumination region to which the light emitted from the illuminating optical system is applied. That is, in illuminating optical systems each emitting the same amount of illumination light, the illuminance increases in the illuminating optical system having a small area of the illumination region to which the illumination light is applied, whereby the image displayed by the projector is brightened. Therefore, the illuminating optical system of the projector may preferably have high illumination efficiency to a light application surface of the electrooptic device. However, when an optical modulation device (emitting direction control-type optical modulation device), such as the DMD, is used as an electrooptic device for the projector, there is a problem in that illumination efficiency of the illuminating optical system is decreased by the positional relationship between the illuminating optical system and the optical modulation device. In addition, this problem also occurs in optical modulation devices for controlling the direction of emission of illumination light applied to a light application surface (including a plurality of pixels) according to image information (for each pixel) to thereby emit image light representing an image.
It is one aspect of this invention to provide a technique for achieving a reduction in size of a projector using an optical modulation device (emitting direction control-type optical modulation device) for controlling a direction of emission of illumination light applied to a light application surface for each pixel according to image information to thereby emit image light representing an image, by shortening a length of an optical path (physical length of an optical path between a light source and the emitting direction control-type optical modulation device) of an illuminating optical system as compared to that of a conventional illuminating optical system. In addition, it is a second object of this invention to provide a technique for achieving an increase in illumination efficiency of the illuminating optical system.
In order to solve at least a part of the above-described problems, in accordance with the first aspect of the present invention, there is provided a projector, that may include an illuminating optical system for emitting illumination light, an optical modulation device for modulating the illumination light emitted from the illuminating optical system, and a projection optical system for projecting light emitted from the optical modulation device, wherein the optical modulation device is an emitting direction control-type optical modulation device for controlling a direction of emission of illumination light applied to a light application surface of the optical modulation device according to a given image signal to modulate the illumination light, thereby emitting image light representing an image.
The illuminating optical system may include a light source, a first lens array having a plurality of first small lenses for dividing light emitted from the light source into a plurality of partial light beam fluxes, and a second lens array having a plurality of second small lenses corresponding to the plurality of first small lenses.
The plurality of partial light beam fluxes divided by the first lens array are applied onto the entire light application surface of the optical modulation device via the second lens array, respectively. That is, the first lens array and the second lens array have the function of uniformly illuminating the light application surface of the optical modulation device, similarly to a light-transmitting rod used in a conventional illuminating optical system.
A length of an optical path of the illuminating optical system including the first lens array and the second lens array (physical length between the light source and the optical modulation device) can be easily adjusted according to setting of lens characteristics of the lens arrays. For this reason, the length of the optical path of the illuminating optical system can be easily shortened, as compared to the conventional illuminating optical system using the light-transmitting rod, whereby the size of a projector of the first aspect can be easily reduced, as compared to a conventional projector.
In the above-described projector of the first aspect, at least one of the plurality of first small lenses of the first lens array may be a decentering lens. In addition, at least a part of the plurality of second small lenses of the second lens array may be a decentering lens. If at least one of the plurality of first small lenses of the first lens array and at least one of the plurality of second small lenses of the second lens array is a decentering lens that is set according to a direction of light incident thereon, the partial light beam flux emitted therefrom can be efficiently applied to the light application surface of the optical modulation device.
In the above-described projector of the first aspect, the illuminating optical system may preferably include a first condenser lens, a color wheel having a plurality of color filters rotatably formed thereon, and a second condenser lens in order between the light source and the first lens array.
In addition, the illuminating optical system may include a first condenser lens, a color wheel having a plurality of color filters rotatably formed thereon, and a second condenser lens in order between the second lens array and the optical modulation device.
With these arrangements, it is possible to facilitate a reduction in the size of optical systems constituting a projector for displaying a color image.
In accordance with a second aspect of the present invention, there is provided a projector that may include an optical modulation device for controlling a direction of emission of illumination light applied to a substantially rectangular light application surface, including a plurality of pixels, for each pixel according to image information to thereby emit image light representing an image, an illuminating optical system for emitting the illumination light so that the central axis of the illumination light applied to the light application surface enters the light application surface at a predetermined angle, and a projection optical system for projecting image light emitted from the optical modulation device.
The illuminating optical system may include an optical element such that an outline shape of an emitting surface is a quadrilateral having first and second diagonal lines of different lengths, and when the illumination light emitted from the optical element obliquely enters the light application surface at the predetermined angle, the quadrilateral is set so that the ratio of two diagonal lines of a quadrilateral illumination region to which the illumination light is applied is closer to 1 than the ratio of the lengths of the first and second diagonal lines.
According to the above-described projector of the second aspect, the outline shape of the illumination region can be brought closer to the substantially rectangular light application surface even if the illumination light obliquely enters the light application surface at a predetermined angle. Therefore, the illumination efficiency of the illumination light applied to the light application surface of the optical modulation device can be increased.
In the above-described projector of the second aspect, the illuminating optical system may preferably include a light source, a first lens array having a plurality of first small lenses each being equivalent to the optical element, and dividing the light emitted from the light source into a plurality of partial light beam fluxes, and a second lens array having a plurality of second small lenses corresponding to the plurality of first small lenses.
With these arrangements, the illumination efficiency of each of the plurality of partial light beam fluxes applied to the light application surface can be increased, and a uniform illuminance distribution of the illumination light applied to the light application surface can be produced.
Incidentally, each of the plurality of first lenses may be a lens having a parallelogram-shaped outline. With this arrangement, the plurality of first small lenses can be closely arranged without any spaces, so that the light emitted from the light source entering the first lens array can be used more effectively by being divided into a plurality of partial light beam fluxes.
Here, at least one of the plurality of first small lenses of the first lens array may be a decentering lens. In addition, at least one of the plurality of second small lenses of the second lens array may be a decentering lens. If at least one of the plurality of first small lenses of the first lens array and at least a part of the plurality of second small lenses of the second lens array is a decentering lens that is set according to a direction of light incident thereon, the partial light beam flux emitted therefrom can be efficiently applied to the light application surface of the optical modulation device.
In the above-described projector of the second aspect, the illuminating optical system may preferably include a first condenser lens, a color wheel having a plurality of color filters rotatably formed thereon, and a second condenser lens in order between the light source and the first lens array.
In addition, the illuminating optical system may include a first condenser lens, a color wheel having a plurality of color filters rotatably formed thereon, and a second condenser lens in order between the second lens array and the optical modulation device.
With these arrangements, it is possible to facilitate a reduction in the size of optical systems constituting a projector for displaying a color image.
Incidentally, in the above-described projector of the second aspect, the illuminating optical system may preferably include a light source, and a light-transmitting rod equivalent to the optical element.
With these arrangements, the illumination efficiency of the illumination light applied to the light application surface can also be increased, and a uniform illuminance distribution of the illumination light applied to the light application surface can be produced.